Herpes simplex viruses infect their hosts for life, causing cold sores (HSV-1), eye and genital infections (HSV-1 and -2), and encephalitis. Furthermore, they can wreak havoc in immuno-compromised individuals or in newborns. Host cell entry by HSV-1 requires four viral envelope glycoproteins: gB, gD, and gH/gL complex. Binding of gD to a cell-surface receptor, which triggers fusion events, has been studied crystallographically. By contrast, no structural information is available on the other three proteins, and little is known about how they participate in cell entry. Knowing the structures of all the components of the membrane fusion machinery is a necessary step in unveiling the mechanism of HSV cell fusion. Our long-term goal is to elucidate the mechanism of Herpes virus entry into host cells at the atomic level and to use this knowledge to design effective inhibitors of viral entry into cells for preventative and therapeutic purposes. In preliminary studies, we have crystallized the ectodomain of gB and are currently determining its structure. In this application we propose biochemical and structural studies of additional domains and larger forms of gB, in order to build a more complete picture of its activities and interactions The three specific aims are 1) to determine the structure of the cytoplasmic domain of gB; 2) to produce pure, soluble forms of gB encompassing multiple domains for structural studies; and 3) to study the mechanism of the antiviral effect of a G-quartet oligonucleotide crystallographically. This structural information will provide the framework for elucidating the function of gB in cell entry. For example, known functional mutations will be mapped onto the structure. Moreover, strategies developed for producing soluble multidomain forms of gB for structural studies will allow us to approach gH/gL and, eventually, to assemble multi-protein complexes.